The launch of the Indian communications satellite GSAT-5P (INSAT 4D) ended in failure when its GSLV-F06 carrier rocket veered off course and started disintegrating shortly after lift-off.

"Controllability of the vehicle was lost after about 47 seconds because we found the control command did not reach the actuators," said K. Radhakrishnan, chairman of the Indian Space Research Organisation.

The design of the GSLV's first stage is somewhat unusual: it consists of a solid propellant core and four liquid propellant strap-ons. Flight control is achieved through engine gimbaling on the strap-ons.

"What has caused this interruption at 47 seconds has to be studied in detail," Dr. Radhakrishnan said. Without flight control, the rocket "developed large amplitude errors relating to higher angle of attack," causing the vehicle to break up. Additionally, a self destruct command was sent 63 seconds after lift-off. The debris fell safely into the Bay of Bengal.

The Hindu quoted Dr. Radhakrishnan as saying that control signals from the Equipment Bay, located above the upper stage, "did not reach the actuator system in the first stage of the vehicle... We suspect that a connector chord, which takes the signal down, has snapped."

The GSLV-F06 failure analysis committee concluded that the mishap was caused by a shroud (a cylindrical cover) between the rocket's second and third stage.

Committee chairman and former ISRO chairman G. Madhavan Nair was quoted as saying that "There is a need for correction in the design of the shroud. The shroud at the bottom of the cryogenic stage did not fulfil all service conditions during the flight, as a result of which the connectors linked to the shroud snapped. The connectors were linked to the shroud."

"The shroud was influenced by the pressure distribution that built up in the flight at around 46 seconds and was distorted. It is the distortion of the shroud that led to pulling out of the connectors, which shouldn't have happened before the separation of the stage. But since it did, the vehicle (GSLV) lost altitude and control as a signal to the strap-ons from the computer did not come, owing to the snapping of the connectors," Dr. Nair said.

Two key recommendations have been made: either make the shroud stronger/tougher or do away with it altogether. "The second is a possibility which we need to work out. If that is possible, all other parameters of the GSLV are fine. A successful flight of the GSLV is not an impossibility," Dr. Nair said.